Every package or parcel seized by an officer or employee of the Postal Service performing duties related to the inspection of postal matters, a customs officer, or United States marshal or his deputies, in which a letter is unlawfully concealed, shall be forfeited to the United States. The same proceedings may be used to enforce forfeitures as are authorized in respect of goods, wares, and merchandise forfeited for violation of the revenue laws. Laws for the benefit and protection of customs officers making seizures for violating revenue laws apply to officers and employees making seizures for violating the postal laws.